The depth of well bores being drilled continues to increase as the number of shallow depth hydrocarbon-bearing earth formations continues to decrease. These increasing well bore depths are pressing conventional drill bits to their limits in terms of performance and durability. Several drill bits are often required to drill a single well bore, and changing a drill bit on a drill string can be both time consuming and expensive.
In efforts to improve drill bit performance and durability, new materials and methods for forming drill bits and their various components are being investigated. For example, methods other than conventional infiltration processes are being investigated to form bit bodies comprising particle-matrix composite materials. Such methods include forming bit bodies using powder compaction and sintering techniques. The term “sintering,” as used herein, means the densification of a particulate component and involves removal of at least a portion of the pores between the starting particles, accompanied by shrinkage, combined with coalescence and bonding between adjacent particles. Such techniques are disclosed in U.S. patent application Ser. No. 11/271,153, filed Nov. 10, 2005, now U.S. Pat. No. 7,802,495, issued Sep. 28, 2010, and U.S. patent application Ser. No. 11/272,439, also filed Nov. 10, 2005, now U.S. Pat. No. 7,776,256, issued Aug. 17, 2010, both of which are assigned to the assignee of the present invention, and the entire disclosure of each of which is incorporated herein by this reference.
An example of a bit body 50 that may be formed using such powder compaction and sintering techniques is illustrated in FIG. 1. The bit body 50 may be predominantly comprised of a particle-matrix composite material 54. As shown in FIG. 1, the bit body 50 may include wings or blades 58 that are separated by junk slots 60, and a plurality of PDC cutting elements 62 (or any other type of cutting element) may be secured within cutting element pockets 64 on the face 52 of the bit body 50. The PDC cutting elements 62 may be supported from behind by buttresses 66, which may be integrally formed with the bit body 50. The bit body 50 may include internal fluid passageways (not shown) that extend between the face 52 of the bit body 50 and a longitudinal bore 56, which extends through the bit body 50. Nozzle inserts (not shown) also may be provided at the face 52 of the bit body 50 within the internal fluid passageways.
An example of a manner in which the bit body 50 may be formed using powder compaction and sintering techniques is described briefly below.
Referring to FIG. 2A, a powder mixture 68 may be pressed (e.g., with substantially isostatic pressure) within a mold or container 74. The powder mixture 68 may include a plurality of hard particles and a plurality of particles comprising a matrix material. Optionally, the powder mixture 68 may further include additives commonly used when pressing powder mixtures such as, for example, organic binders for providing structural strength to the pressed powder component, plasticizers for making the organic binder more pliable, and lubricants or compaction aids for reducing inter-particle friction and otherwise providing lubrication during pressing.
The container 74 may include a fluid-tight deformable member 76 such as, for example, a deformable polymeric bag and a substantially rigid sealing plate 78. Inserts or displacement members 79 may be provided within the container 74 for defining features of the bit body 50 such as, for example, a longitudinal bore 56 (FIG. 1) of the bit body 50. The sealing plate 78 may be attached or bonded to the deformable member 76 in such a manner as to provide a fluid-tight seal therebetween.
The container 74 (with the powder mixture 68 and any desired displacement members 79 contained therein) may be pressurized within a pressure chamber 70. A removable cover 71 may be used to provide access to the interior of the pressure chamber 70. A fluid (which may be substantially incompressible) such as, for example, water, oil, or gas (such as, for example, air or nitrogen) is pumped into the pressure chamber 70 through an opening 72 at high pressures using a pump (not shown). The high pressure of the fluid causes the walls of the deformable member 76 to deform, and the fluid pressure may be transmitted substantially uniformly to the powder mixture 68.
Pressing of the powder mixture 68 may form a green (or unsintered) body 80 shown in FIG. 2B, which can be removed from the pressure chamber 70 and container 74 after pressing.
The green body 80 shown in FIG. 2B may include a plurality of particles (hard particles and particles of matrix material) held together by interparticle friction forces and an organic binder material provided in the powder mixture 68 (FIG. 2A). Certain structural features may be machined in the green body 80 using conventional machining techniques including, for example, turning techniques, milling techniques, and drilling techniques. Hand-held tools also may be used to manually form or shape features in or on the green body 80. By way of example and not limitation, blades 58, junk slots 60 (FIG. 1), and other features may be machined or otherwise formed in the green body 80 to form a partially shaped green body 84 shown in FIG. 2C.
The partially shaped green body 84 shown in FIG. 2C may be at least partially sintered to provide a brown (partially sintered) body 90 shown in FIG. 2D, which has less than a desired final density. Partially sintering the green body 84 to form the brown body 90 may cause at least some of the plurality of particles to have at least partially grown together to provide at least partial bonding between adjacent particles. The brown body 90 may be machinable due to the remaining porosity therein. Certain structural features also may be machined in the brown body 90 using conventional machining techniques and hand-held tools.
By way of example and not limitation, internal fluid passageways (not shown), cutting element pockets 64, and buttresses 66 (FIG. 1) may be machined or otherwise formed in the brown body 90 to form a brown body 96 shown in FIG. 2E. The brown body 96 shown in FIG. 2E then may be fully sintered to a desired final density, and the cutting elements 62 may be secured within the cutting element pockets 64 to provide the bit body 50 shown in FIG. 1.
In other methods, the green body 80 shown in FIG. 2B may be partially sintered to form a brown body without prior machining, and all necessary machining may be performed on the brown body prior to fully sintering the brown body to a desired final density. Alternatively, all necessary machining may be performed on the green body 80 shown in FIG. 2B, which then may be fully sintered to a desired final density.
As sintering (such as sintering of powder mixture 68 (FIG. 2A) to form brown body 96 (FIG. 2E)) involves densification and removal of porosity within a structure, the structure being sintered will shrink during a sintering process. As a result, dimensional shrinkage may need to be considered and accounted for when designing tooling (molds, dies, etc.) or machining features in structures that are less than fully sintered.
The positions of the cutting elements 62, which are secured within the cutting element pockets 64, relative to one another and to the bit body 50 are critical to performance of the drill bit (e.g., bit stability, durability, and rate of penetration) during drilling operations. If the cutting element pockets 64 are not properly located on the bit body 50, the performance of the drill bit may be negatively affected.
For example, if a cutting element 62 protrudes as little as 2.54 millimeters (one-tenth of an inch ( 1/10″)) beyond the design position, that particular cutting element 62 may be exposed to an increased workload and increased forces during drilling. Such increased workload and forces may lead to early failure of the cutting element 62 and possibly the entire drill bit.
Furthermore, when the cutting elements 62 are displaced from their designed positions they may cause dynamic stability and performance problems. For example, cutting elements 62 that are displaced from their design positions may cause a drill bit to rotate about a rotational axis offset from the longitudinal axis of the drill bit in such a way that the drill bit tends to wobble or “whirl” in the borehole. This whirling may cause the center of rotation to change dramatically as the drill bit rotates within the borehole. Thus, the cutting elements 62 may travel faster, sideways, and contact the wellbore at undesired angles and locations and thus may be subject to greatly increased impact loads that may cause the failure of the cutting elements 62.
The positions of the cutting element pockets 64 relative to one another and to the bit body 50 may change during a sintering process, such as that described above, as the bit body 50 shrinks. In other words, for a given desired final bit design, if the corresponding green or brown bit body is formed according to uniformly scaled dimensions of the final bit design, the relative positions of the cutting element pockets 64 on the constructed bit body 50 may not accurately correspond to the design of the bit body. Additional machining of the bit body 50 (FIG. 1) in the fully sintered state may be required in some cases to account for the error in the position of the cutting element pockets 64 due to shrinking during sintering. However, machining of the bit body 50 (FIG. 1) in the fully sintered state may be difficult due to the hardness, wear-resistant and abrasive properties of the particle-matrix composite material 54 from which the bit body 50 is formed. Such shrinkage during sintering may be encountered with features of the bit body 50 other than cutting element pockets 64 such as, for example, fluid courses, nozzle recesses, junk slots, etc.